A first type of general ophthalmic lens generating apparatus has a cup-shaped abrading tool repeatedly sweeping across the surface of a lens blank until the prescribed curvature is obtained. The cup-shaped abrading tool is affixed to a slide plate movably mounted on a swing arm. The center of rotation of the swing arm is movable towards and away from a lens blank holder and the length of the swing arm is adjustable. The slide plate is movable about a pivot which is coaxial with the center of radius of the edge of the abrading cup. The base curve on the ophthalmic lens is determined by the length of the swing arm, and the cross curve is determined by the angular relationship of the abrading tool relative to the axis of the lens blank.
Various inventions pertaining to ophthalmic lens generating apparatus of the first type are illustrated and described in the following U.S. Patents:
U.S. Pat. No. 3,458,956 issued on Aug. 5, 1969 to J. M. Suddarth et al; PA0 U.S. Pat. No. 4,068,413 issued on Jan. 17, 1978 to J. M. Suddarth; PA0 U.S. Pat. No. 4,419,846 issued on Dec. 13, 1983 to G. Schimitzek et al; PA0 U.S. Pat. No. 4,574,527 issued on Mar. 11, 1986 to R. S. Craxton; PA0 U.S. Pat. No. 4,653,233 issued on Mar. 31, 1987 to E. Brueck; PA0 U.S. Pat. No. 4,866,884 issued on Sep. 19, 1989 to K. L. Smith et al; PA0 U.S. Pat. No. 5,181,345 issued on Jan. 26, 1993 to S. Kulan. PA0 U.S. Pat. No. 4,493,168 issued on Jan. 15, 1985 to E. L. Field, Jr.; PA0 U.S. Pat. No. 4,908,997 issued on Mar. 20, 1990 to E. L. Field, Jr. et al; PA0 U.S. Pat. No. 5,485,771 issued on Jan. 23, 1996 to Brennan et al. PA0 a) moving the lens holder near a far end of the second linear slide with the ophthalmic lens being positioned on one side of the horizontal longitudinal axis and having a far edge and a near edge relative to the horizontal longitudinal axis; PA0 b) rotating the rotary table such that the rotatable arbor of the tool spindle is oriented in a vicinity of a parallel alignment with the horizontal transversal axis; PA0 c) moving the first movable support such that the cutting side of the lens surfacing tool is near one of the far and near edges of the ophthalmic lens; PA0 d) rotating the lens surfacing tool and moving the first movable support for moving the cutting side of the lens surfacing tool in contact with the ophthalmic lens; PA0 e) simultaneously rotating the rotary table and actuating the first linear actuator for sweeping the cutting side of the lens surfacing tool along a prescribed base curve across the optical surface of the ophthalmic lens.
A second type of ophthalmic lens generating apparatus of the prior art is characterized by the use of a computer and linear servo-actuators for moving the tool or the lens holder during the lens generating process. The prescribed curvature on the ophthalmic lens is obtained by interpolating and simultaneously guiding the motions of the linear actuators.
Examples of computer-controlled lens generating apparatus of the prior art are provided in the following U.S. Patents:
In the lens generating apparatus of the first type, the advance of the abrading tool towards the surface of the lens is directly related to the extension of the swing arm or to the height of the arc defined by the sweeping of the tool against the surface of the lens blank. Similarly, in the computer-controlled lens generating apparatus, the precision of a displacement of the abrading tool in a direction generally perpendicular to a plane defined by a lens blank is directly related to a smallest increment of the linear actuator moving the tool in this direction. Therefore, any defect in the mechanism for articulating or extending the swing arm in the apparatus of the first type as well as any defect in the linear actuators of a computer-controlled apparatus has a direct effect on the quality of the surface being generated by these machines.
Although ultra-smooth mechanisms and servo-actuators are available commercially, the level of precision required by the optical industry generally exceeds the most stringent precision requirement by industrial sectors. Consequently, it has been generally accepted that an ophthalmic lens generated on the apparatus of the prior art requires extensive fining and polishing of the surface of the lens for correcting focal errors in the generated lens and for obtaining a proper transparency of the lens' surface.